1. Field of the Invention
This invention relates to an improvement in the synthesis of hydrogen peroxide from hydrogen and oxygen and, more particularly, to a process in which improved yields of hydrogen peroxide are attained along with an unexpected increase in catalyst life.
2. Prior Art
The synthesis of hydrogen peroxide from hydrogen and oxygen in aqueous systems containing an oxygen-containing organic cosolvent and an aqueous acid or acids, in the presence of a Group VIII metal catalyst on a support, has been proposed by Hooper in U.S. Pat. Nos. 3,361,533 and 3,336,112. These references disclose using hydrogen and oxygen at ratios close to 1:1, as required by stoichiometry: EQU H.sub.2 +O.sub.2 .fwdarw.H.sub.2 O.sub.2
It has been proposed by Kim et al., in U.S. Pat No. 4,007,256, that a solvent system containing an organic nitrogen compound, a strong acid and water can be used for the synthesis of hydrogen peroxide in the presence of a palladium catalyst on a solid support. In data derived from batch studies in acetonitrile:water 85:15, varying the hydrogen/oxygen ratio from 2:1 to 1:0.33, improvement in both hydrogen peroxide yield and in selectivity to hydrogen peroxide was found at lower hydrogen/oxygen ratios.
Izumi (U.S. Pat. No. 4,009,252) has proposed preparing hydrogen peroxide in an essentially aqueous medium, using a platinum-group catalyst while maintaining partial pressures of hydrogen and oxygen of at least 0.5 and 1.0 atmospheres, respectively. It is preferred that the oxygen/hydrogen ratio be 2.0-10. The reference states that the amount of catalyst per volume of solution should not exceed 30 mg., calculated as metal, per 100 ml. of aqueous medium. Preferably, the amount of catalyst is 0.1-20 mg., as metal, per 100 ml. of solution. Moreover, in order to avoid danger of explosion at high pressures of hydrogen and oxygen, the use of an inert diluent gas is recommended. This process is economically not practical due to the low solubility of hydrogen in water, particularly at low hydrogen partial pressures and the low levels of catalyst charge (&lt;30 mg./100 cc.) indicated as being tolerable. British Pat. No. 1,490,925 proposes a similar process for synthesizing hydrogen peroxide.
In British Pat. No. 1,546,129, an improved method for synthesizing hydrogen peroxide, under generally similar conditions, is proposed. A continuous reaction, in which the gas and liquid zones of the reactor were constantly stirred, was described. However, the catalyst must be pretreated with hydrogen before exposure to the reaction medium. This process accordingly becomes operationally very complex on a commercial scale.
The instant invention overcomes the limitations of prior art processes in a simple manner while also greatly extending the useful catalyst life, a problem with all the above processes.